1. Field
Embodiments relate to a walking robot which walks using a plurality of legs and a control method thereof.
2. Description of the Related Art
Robots are machines which perform a motion similar to that of humans. Initial robots were industrial robots, such as manipulators or transfer robots for the purposes of automation and unmanned operation. Recently, research and development of walking robots which mimic bipedal walking of humans has progressed. Bipedal walking is disadvantageous in that it is unstable and is difficult in terms of pose control and walking control compared with tripedal walking or hexapedal walking, but is advantageous in that it more flexibly copes with the uneven ground or discontinuous surfaces.
Control of walking robots is generally divided into a position-based Zero Moment Point (ZMP) control method and a torque-based Finite State Machine (FSM) control method.
In the ZMP control method, a walking direction, a walking stride, and a walking velocity of a walking robot are set in advance, walking patterns of respective legs corresponding to the set factors are generated, and walking trajectories of the respective legs are calculated based on the walking patterns. Further, in case of a bipedal walking robot, target control values of motors of respective joints are calculated through calculation of inverse Kinematics of the calculated walking trajectories. Further, servo control in which the respective legs trace the calculated walking trajectories is carried out. Therefore, it is detected whether or not positions of the respective legs precisely trace the walking trajectories based on the walking patterns during walking, and if the respective legs deviate from the walking trajectories, torques of motors are adjusted so that the respective legs precisely trace the walking trajectories. On the other hand, in the FSM control method, FSMs and states of respective motions of a walking robot are defined in advance, and the robot is controlled so as to properly walk according to the respective states of the motions during walking.
The ZMP control method is a position-based control method and thus achieves precise position control, but requires a high servo gain, thereby having low energy efficiency and high stiffness and resulting in a great impact applied to surrounding environments. The FSM control method achieves control through a torque command and is applied to an elastic mechanism and thus has high energy efficiency and low stiffness and is safe with respect to surrounding environments, but cannot perform precise position control and thus has difficulty in performing a precise whole body motion, such as stair ascent or obstacle avoidance.
Therefore, walking robots may be controlled through different walking servo control methods according to various conditions, such as walking environments, performance of the robots, etc., and require combination of various servo control methods. However, if conversion between the different servo control methods is not carefully performed, joints of the robot may sag due to a stiffness difference between the servo control methods, possibly resulting in hardware damage.